This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Small-angle x-ray fiber diffraction is the method of choice to obtain structural information at the same time as physiological information from working muscle. A significant barrier to progress is the susceptibility of muscle to radiation damage at the high x-ray dose rates typical at beamline 18ID. The main strategy available to mitigate radiation damage is to use a relatively large sample and scan it in the beam during the exposure. This isn't possible with small samples such as those isolated form the hearts of rodents so some other way of reducing damage is clearly needed. Anecdotal information from researchers at Spring-8 in Japan have indicated that living muscles last much longer at 15 keV than at 12 keV but this has not been documented in the peer reviewed literature. Here we explored the possibility of using 18 ID to do muscle experiments at 15 keV and to see if this had appreciable effects on sample lifetimes